Method for Representing a Participating Media in a Scene and Corresponding Device

1. A method of displaying an image representative of a virtual scene comprising a participating media, the participating media being delimited by a bounding box, said participating media rendered from a viewpoint at a determined distance from the viewpoint according to a viewing direction, wherein the method comprises: for at least one point of a volume formed by said bounding box, determining a set of directions having for origin said at least one point distributed according to at least one half-sphere of which a base is centered on said at least one point; for each direction of at least one part of the set of determined directions, determining a first intersection point, corresponding to the intersection between said direction and said participating media, for which an associated density value is greater than a first threshold value, said first intersection point being determined by starting from a second intersection point corresponding to the intersection between said direction and said bounding box; determining third intersection points, corresponding to the intersections between said viewing direction and said participating media, from an item of information representative of distances separating the first intersection point from the second intersection point for each direction of the at least one part of the of determined directions, said item of information representative of distances being stored in a memory; and displaying pixels of said image, light values associated with said pixels being calculated according to said third intersection points.

2. The method according to claim 1 , further comprising determining projection coefficients in a functions base from values representative of a distance separating the first intersection point from the second intersection point, said item of information representative of distances corresponding to the determined projection coefficients.

3. The method according to claim 2 , wherein said functions base is a spherical functions base.

4. The method according to claim 1 , wherein the distance separating said participating media from said viewpoint according to the viewing direction being greater than a second threshold value, said at least one point of the volume formed by said bounding box corresponds to a center of the bounding box, the set of determined directions being distributed according to a sphere centered on the center of the bounding box.

5. The method according to claim 1 , wherein, the distance separating said participating media from the viewpoint according to the viewing direction being less than a second threshold value and greater than a third threshold value, the method comprises sampling a surface of said bounding box into a plurality of samples, a set of directions being determined for a plurality of points corresponding to at least a part of the plurality of samples, each set of directions being determined according to a half-sphere centered on a considered sample of the plurality of samples, the base of the half-sphere belonging to the surface of the bounding box, the half-sphere being oriented toward the inside of said bounding box, the third intersection points are moreover determined from a fourth intersection point corresponding to the intersection between the viewing direction and the bounding box.

6. The method according to claim 5 , wherein when the fourth intersection point does not correspond to one of the samples of the surface of the bounding box, the method comprises determining a sample of the surface of the bounding box corresponding to the fourth intersection by interpolation of the samples surrounding said fourth intersection point.

7. The method according to claim 1 , further comprising sampling said viewing direction between the determined third intersection points.

8. The method according to claim 1 , wherein said participating media is a heterogeneous participating media.

9. A non-transitory computer-readable medium comprising a computer program product recorded thereon and capable of being run by a processor, including program code instructions for implementing the method according to claim 1 .

10. A device configured to display an image representative of a virtual scene comprising a participating media comprised in a scene, the participating media being delimited by a bounding box, said participating media being rendered from a viewpoint at a determined distance from the viewpoint according to a viewing direction, wherein the device comprises at least one processor configured to: determine, for at least one point of a volume formed by said bounding box, a set of directions having for origin said at least one point and distributed according to at least one half-sphere of which a base is centered on said at least one point; determine, for each direction of at least one part of the set of determined directions, a first intersection point, corresponding to the intersection between said direction and said participating media, for which an associated density value is greater than a first threshold value, said first intersection point being determined by starting from a second intersection point corresponding to the intersection between said direction and said bounding box; determine third intersection points, corresponding to the intersections between said viewing direction and said participating media, from an item of information representative of distances separating the first intersection point from the second intersection point for each direction of the at least one part of the set of determined directions, said item of information representative of distances being stored in a memory; and display pixels of said image, light values associated with said pixels being calculated according to said third intersection points.

11. The device according to claim 10 , wherein the at least one processor is further configured for estimating to determine projection coefficients in a functions base from values representative of a distance separating the first intersection point from the second intersection point.

12. The device according to claim 11 , wherein said functions base is a spherical functions base.

13. The device according to claim 10 , wherein the at least one processor is further configured for sampling the surface of said bounding box and a plurality samples.

14. The device according to claim 10 , wherein the at least one processor is further configured for sampling said viewing direction between the estimated determined third intersection points.

15. The device according to claim 10 , wherein the distance separating said participating media from said viewpoint according to the viewing direction being greater than a second threshold value, said at least one point of the volume formed by said bounding box corresponds to a center of the bounding box, the set of determined directions being distributed according to a sphere centered on the center of the bounding box.

16. The device according to claim 10 , wherein the distance separating said participating media from the viewpoint according to the viewing direction is less than a second threshold value and greater than a third threshold value, the at least one processor being further configured to: sample a surface of said bounding box into a plurality of samples, a set of directions being determined for a plurality of points corresponding to at least a part of the plurality of samples, each set of directions being determined according to a half-sphere centered on a considered sample of the plurality of samples, the base of the half-sphere belonging to the surface of the bounding box, the half-sphere being oriented toward the inside of said bounding box, the third intersection points is moreover determined from a fourth intersection point corresponding to the intersection between the viewing direction and the bounding box.

17. The device according to claim 16 , wherein when the fourth intersection point does not correspond to one of the samples of the surface of the bounding box, the at least one processor is further configured to determine a sample of the surface of the bounding box corresponding to the fourth intersection by interpolation of the samples surrounding said fourth intersection point.

18. The device according to claim 10 , wherein said participating media is a heterogeneous participating media.